This invention relates to a crankcase ventilation arrangement for a four cycle engine and more particularly to a crankcase ventilation for an outboard motor.
It has been proposed to employ four cycle engines as the power plant in an outboard motor to replace the more conventionally utilized two cycle engine. One reason for this is the more environmentally friendly nature of a four cycle engine caused by the fact that the lubricant for such engine is recirculated rather than discharged along with the combustion products of the engine.
However, four cycle engines present some problems in connection with adaptation to outboard motor application. This is particularly true with respect to the feature which makes them advantageous over two cycle engines. That is, the recirculating lubricating system for a four cycle engine presents some problems in connection with placement, operation and location within outboard motors. This is primarily due to the extremely compact nature of an outboard motor.
It is also known to employ a crankcase ventilation arrangement for engines wherein the blowby gases from the cylinders are utilized to not only ventilate the engine but also are returned to the induction system rather than being discharged to the atmosphere. This minimizes the number of hydrocarbons that are emitted to the atmosphere.
However, in connection with the return of the crankcase blowby gases to the induction system, this must be done in such a way that it is ensured that any oil in the crankcase gases can be condensed and returned back to the lubrication system rather than deliver to the engine induction system. With the space available in the power head of an outboard motor, this means that it may be difficult to provide the effective separation of the oil from the crankcase blowby gases before it is introduced to the engine through its induction system.
It is, therefore, a principal object of this invention to provide an improved crankcase ventilation arrangement for an outboard motor.
It is a further object of this invention to provide an outboard motor crankcase ventilating arrangement that provides a long flow path to ensure good separation and nevertheless permits the gases to be delivered to the engine through its intake system.
In connection with the delivery of the crankcase gases to the engine combustion chambers for further combustion of any hydrocarbons therein, the return should be such that the crankcase gases are delivered substantially uniformly to each cylinder of a multiple cylinder engine. This is desirable to ensure that each cylinder experiences substantially the same combustion characteristics. This presents another problem that is unique to outboard motors.
In outboard motors, it is the general practice to position the engine so that the crankshaft rotates about a vertically disposed axis. This means that in multi-cylinder engines, the cylinders are placed one vertically above the other. This presents unique problems in ensuring that the crankcase ventilating gases that are returned to the engine through its induction system are uniformly distributed.
The hydrocarbons which may be present in the crankcase ventilating gases can cause the crankcase ventilating gases to have a greater density that the atmospheric air. Thus, the vertical disposition of the cylinders might tend to cause an arrangement wherein the lowermost cylinders receive a higher proportion of the crankcase ventilating gases in the uppermost cylinder.
It is, therefore, a still further object of this invention to provide an improved crankcase ventilating system for an outboard motor wherein the crankcase ventilating gases are distributed equally to the cylinders of the engine for further combustion of hydrocarbons therein.